Our studies to date have indicated the effectiveness of medium- titer ZIG for attenuation of varicella in exposed susceptibles at a level as low as .015 ml./kg. and of low-titer ZIG at a level of .02 ml./kg. in patients in 2 risk groups: those debilitated by acute or chronic illness and in the age groups subject to the hazard of varicella complications; and of medium-titer ZIG at the level of .05 ml./kg. for attenuation in high-risk, immunosuppressed patients. The maximum dosage used, 0.15 ml./kg., has been found to be largely but not completely preventive in debilitated and high-risk patients. We will now study the medium-titer ZIG at a lower level,.01 ml./kg., for attenuation, and at levels greater than or equal to 0.15 ml./kg. for prevention. Adenine arabinoside (vidarabine) studies in active complications of varicella-zoster and herpes simplex infection have uncovered the existence of several forms of moderate reversible toxicity, which must be considered in patient selection and which are probably related to the levels of 15 mg./kg./ day and above. These studies will be continued. Bibliographic references: Zoster immune globulin: regional production and allocation. Avron H. Ross, S. Wayne Klein, Barbara McKennett, Anita Kaminer and Karen Caifa. N.Y.S. Journal of Medicine 74:1367-1372, 1974. Toxicity of adenine arabinoside in humans. Avron H. Ross, Antonio Julia and C. Balakrishnan. Abstract. Symposium on Antivirals with Clinical Potential. Stanford University, August 26-29, 1975.